Track circuits



June 14, 1960 L. DUTEIL 2,941,069

TRACK CIRCUITS Filed April 17, 1957 I 2 Sheets-Sheet 1 r --1 N l I l I k155i Figri.

To filylzalilzg Appalmus F INVENTOR.

Louis Dwiezl BY MAM HIS A TTORNE'Y L. DUTEIL TRACK CIRCUITS June 14, 1960 Filed April 17, 1957 2 Sheets-Sheet 2 INVENTOR. Louis Dated By [a L W HIS ATTORNEY United States Patent "ice This invention relates to traflic controls, and more particularly to an improvedtrack circuit'for usegin railway signaling systems.

Inorder to employ conventional track circuits for operating signaling systems for railroadtracks it is required that successive track sections be insulated from each other by insulating joints. In certain instances, inductive means must be connected across the insulating joints in order to provide an electrical path for the motive power.

Accordingly, it is an object of the present invention to provide a track circuit which maybe employed in a track section having no insulating joints and comprising electrically continuous rails, and which track circuit delimits clearly the controlled zone in said electrically continuous rails.

A track circuit according to the present invention provides obvious advantages when employed with all types of track rails and particularly when employed with relatively long track rails.

7 Further, the track circuit according to the present invention may be superimposed on an existingsignal system without interfering with or being interfered with by said existing signal system, and may be adapted to control, for example, grade crossing signals.

' The present invention is based on the principle that the inductive effect of the track rails is proportional to the length of the track and becomes more pronounced as the frequency increases. The inductive effect of the rails makes possible the combination of the inductance therein with an introduced capacity so as to establish a resonant circuit which may be employed in the operation of the track circuit of the present invention. Any modification of the length of the track rails, as measured from the points on the rails at which an oscillator is connected, involves a modification of the inductive component of the circuit and can have the effect of influencing operation of the oscillator. The inductance of the track rails may be modified due particularlyto the presence of railroad car wheels on said rails in the vicinity where the oscillator circuit is connected to the rails. The car wheels act to shunt the track rails and effectively gradually reduce the apparent length of the track.

More specifically, it is an object of the'present invention to provide a track circuit for a track section comprising electrically continuous rails, the track circuit being connected to said rails at two pairs of spaced points located at a predetermined distance from one another. The track circuit includes two resonant or oscillating circuits; the self inductance of each of the resonant circuits forms a part, respectively, of two transformers which couple to an oscillator of the vacuum tube or transistor type. The oscillator is adapted to operate a relay which in turn is adaptedto actuate control circuitry of railroad signaling apparatus.

It is another object of the present invention to provide a track circuit including an oscillator and in which the track rails form a part of at least one of the resonant 2,941,069 Patented June 14, 19 0 circuits of said oscillator. Said one resonant circuit may be a series resonant circuit tuned to the operating frequency of the track circuit.

It is another object of the present invention to provide a track circuit for a track of the type mounted on metallic ties. In that zone of the track rails across which the track circuit is connected or branched off, the metallic ties are replaced by Wooden ties and at each end of the said zone a short-circuiting bar is afiixed between the rails for thepurpose of providing a short-circuit of the metallic ties. A condenser may be included'between the brancholf points of at least one of the oscillating circuits.

The track circuit according to the present invention will be described for the case in which the circuit is superimposed on an already existing signaling circuit, and as an example, particularly for the case in which the track circuit of the present invention is employed in the control of railway grade crossing signals.

Heretofore, trains have usually been announced at grade crossing by the operation of one or two treadles before, and at a great distance from, the grade crossing and its release by a treadle after, and at a small distance from, the grade crossing. It may happen that a train has for some reason been stopped before a grade crossing but that some car wheels have already operated the release treadle causing the gates to open prematurely.

Accordingly, it is anotherobject of the present invention to provide a track circuit to eliminate the aforementioned danger of having the grade crossing gates open while a train is still in the grade crossing.

The track circuit of the present invention affords continuous protection, and not a point to point protection as provided by the treadle actuated controls of the prior art. The length of the track circuit according to the present invention can be, for example, in the order of 2040 meters. The length may vary according to the conditions and the purposes for which the circuit is emplayed.

The operation of the oscillator of the track circuit according to the present invention is affected by the resonant circuits formed to include the inductance of the track rails, byrneans of which inductance the oscillator is maintained in oscillation. Any modification of the inductance of the track will involve a change in operation of the oscillator, even to resulting in the stopping of oscillation during those periods when the track rails are occupied by a railroad car or other such vehicle. A relay controlled by the oscillator will either be deenergized, or energized depending on Whether the oscillation has been stopped, or has assumed a certain value, and the relay will in turn cause actuation of the signaling apparatus to one or another condition.

Other characteristics and advantages of the present invention will become apparent from the following description and the accompanying drawings in which like reference numerals indicate like elements throughout, and in which:

Fig. 1 is a diagrammatic view of one embodiment of the track circuit according to the invention,

Fig. 2 is a corresponding view to Fig. 1, representing in a conventional manner the inductances of the rails,

Referring to Fig. l, a section sisting of relatively long, electrically continuous rails 11 and 13 which may be terminated by insulating joints 15 and 17. Inductive connections 19 and 21 of any suitable type may be connected in a conventional manner across the insulating joints 15 and !17, respectively. A wheel and axle unit 23 depicting schematically the wheel and axle unit of a railroad car is shown as positioned on the track rails. A track circuit 25 according to the present invention is connected at the terminal or branch points 27 and 31, and 29 and 33 on the rails 11 and 13, respectively. The track circuit 25 includes an oscillator 35, and a relay 37 connected to, and controlled by, the

of track is shown conoscillator. 'A feedbackpath for the oscillator 35 con- 3 nects from the output portion 30 of the oscillator to terminal points 27 and 29, through the rails 11 and 13 to the terminal points 31 and 33, and thence to' the input portion 32 (see Fig. 2) of the oscillator.

The electrical inductance characteristics of the track rails 11 and 13 are indicated schematically in Fig. 2. The rail 11 is shown as comprising, for purposes here inafter described, an inductance 39 between the points 27 and 31, two inductances 41 and 43 between the joint '15 and point 27, and two inductances 45 and 47 between the point 31 and the joint 17; Likewise, the rail 13 is shown as comprising an inductance 49 between the points 29 and 33,:two inductances 51 and 53 between the joint 19 and point 29, and two inductances 55 and 57 between the point 33 and the joint 21.

A transformer 59 having a primary Winding 63 and a secondary winding 67, and a second transformer 61 having a primary winding 65 and a secondary-winding 69 the other-terminal of which connects to the point 3 1.

It will be understood that the ,track circuit 25 may include either a transistor or a vacuum tube type oscillator. For purposes of this. application it is. deemed suflicient to describe the track circuit 25 as including a transistor type oscillator 35. The oscillator may consist of a conventional P-N-P type transistor having a "common base 73, an emitter 75, and a collector 77. A

suitable source 79 provides the operating potentials to the oscillator 35, A Wiper arm 81 hearing on voltage divider 81, and a variable resistor 88 provide operating adjustments for the oscillator 35, as is well known in the art. The remaining inductive andv capacitive components, not numbered, in the oscillator 35 circuit are conventional, and need not be described further. feedback energy for the oscillator 35 is coupled from the output portion 30 of the oscillator 35 through trans; former 59, through the rails 11 and 13, and through the transformer 61 to the input portion 32 of the oscillator. Thus, the rails 11 and 13 are an integral part of the feedback path for oscillator 35. A transformer 83 having a primary winding 85 and a secondwinding 87 couples the output energyfronrthe oscillator 35 through a full wave rectifier 89 to the relay 37. V

.The secondary winding 67 V and the capacitor 71 together with the inductances of the rails shown, in a diagrammatic manner ,as inductances 39 and49 form a resonant circuit for the portion of the circuit between the terminal points 27 and 29, and the terminal points 31 and 33 while the primary winding 65 of transformer 61 together with the capacitor 73 form with the same inductances another resonant circuit. In operation, and when energized by source 79, the oscillator 35 will oscillate at a frequency determined by the resonant circuits. Oscillator 35 will continue to The "2,941,oe9 I i oscillate so long as the sections of the rails 11 and 13 adjacent the track circuit 25 are unoccupied, that is, so long as no railroad car wheels are on the rails adjacent the track circuit as hereinafter described. The oscillation of the oscillator 35 energizes the relay 37 through the transformer 83 such that a contact 38 of relay 37 is actuated so that associated signaling apparatus will be caused to indicate the track is unoccupied. The signaling apparatus may be of any suitable conventional type not shown.

The presence of a railroad car, shown ,schematically in Fig. 1 as a wheel and axle unit 23, on the track rails 1*1 and 13 shunts the rails and changes the inductive component ofthe resonant circuits in the oscillator 35 feedback path and causes the oscillations-to cease. Stopping the oscillation of the oscillator 35 results in deenergization of the relay 37 and consequent actuation of i the signaling apparatus to indicate that the track is occupied, The shunting action of the car'wheels ceases after the car Wheels have traversed the track circuit from the terminal points 27 and 29 to the terminals points 31 and 33, or-in the reverse direction, and only after'th'e last car' WheelhaS passed the-said terminal points by about 10-15 meters. At the moment the shunting action ceases, the oscillator 35 startsto oscillate and the relay 37 is energized once again to actuate the signaling apparatus to indicate that the track is unoccupied.

The action of any other track circuit existing on the track rails remains unchanged for there is in effect one track circuit superimposed on another circuit of different length; there being no mutual interaction between the circuits due to the fact that the operating frequencies employed may be very different. l

The inductances 39 and 49 of the track rails 11' and '13 form "part, as has been stated before, of aresonant circuit which controls the operation of the oscillator 35; The track rail inductances 43 and 53 and'particularly the points 42 and 52 represent one extreme of the zone where the shunting action of the wheel and axle unit 23 will affect the operating characteristics of the" track circuit 25. The track rail inductances 45 and 55 on the opposite end of the track section and particularly the 9 .ductances 39 and 49, and 45 and 55 is at a maximum at the moment when the shunt exists between the points 46 and 48. Under these conditions the voltage at the left-hand end, as oriented in the figures, of the inductances 45 and 55 which is the. same .as the voltage between branch points 31 and 33, is applied to the primary winding 65 of the coupling transformer 61 throughthe capacitor 73 'whereby'the combinationof the winding 65 and the capacitor 73 is at resonance for the desired operating frequency of the track circuit 25. A large part of the current circulating in the inductances 39 and 49 is diverted into the circuit of the winding 65 and the capacitor 73 and assures the maintenance of oscillations in the oscillator 35 whereby the relay 37 continues to be energized.

Assuming the wheel and axle unit 23 is moving in a direction from left to right as oriented in the drawings the circuit formed by capacitor 71, and ;the inductances 39 and 49 together with the inductances 45 and 55 defines the end of the zone where the shunting action of the wheel and axle unit 23 will affect the track circuit '25. In relation to the movement of the shunt due to the wheel and axle, unit 23 -on that portion of the track represented by the inductances 47 and 57, the intensity of the current in the inductances 39 and 49, and 45 and 55, decreases. However, the voltage across the points 31 and 33 increases because the power required at the transformer 59 is less and becomes stable when the inductive impedance of the track between the points 31 and 33, and the shunt reaches a much higher value than the impedance of the combination consisting of the winding 65 and the capacitor 73.

The effect of a train moving on the track rails in a direction from right to left as oriented in the figures will now beconsidered. When the shunt due to the wheel and axle unit 23 has moved toward the left and is at a position across points 42 and 52, a large current circulates in the inductances 43 and 53 butthe impedance of these inductances is sufiicient to maintain across the points 27 and 29 the voltage necessary for a current to circulate through the inductances 39 and 49 and the circuit including the winding 65. and the capacitor 73, which current provides suflici'ent feedback energy for initiating and maintaining oscillations.

In'relation to the movement of the shunt on that portion of the track represented by the inductances 41 and 51, the current value in the inductances 43 and 53 decreases as the effective shunt moves toward the left. The voltage between the points 27 and 29 increases and becomes stable when the inductive impedance of the track rails between the points 27 and-29 and the shunt is much higher than the. impedance. of. the circuit formed from point 27, through inductance 39, point 31, capacitor 73, winding 65 of transformer 61, point 33, and.induct ance 49 to point 29.

The relay 37 continues to be energized as long as the Shunt'for'mcd by the wheel and axle unit 23 is outside of the zone between the points 42 and 46, and the points 52 and 48. When the shunt formed by the wheel and axle unit 23 is present within the zone between the points 42 and 46, and points 52 and 48, the relay 37 will not be energized causing the signaling apparatus to indicate that the track is occupied.

It should be noted that the capacitors 71 and 73 should present high im'pedances to lower frequencies to prevent those trackcircuits operating at lower frequencies, for example, track circuits for block systems, from influencing the operation of the present circuit.

' An embodiment of the track circuit employed in conjunction with track rails laid on metallic ties 91, as shown in Figs. 3 and 4, will now be considered. To use the track circuit in this environment, it is necessary to replace the metallic ties 91 by wooden ties 93 beginning about 50 meters ahead of the connections of the track circuit to the rails. 1

'.Other track circuits adapted to control relays or any other signaling apparatus such as automatic blocks may be connected in the same zone as is the track circuit of the present invention. Such automatic blocks may be of conventional design and may be operated by means well known in the art, and per se form no part of the present invention. Therefore, the following description will describe only the function of the track circuit according to the present invention.

' As in the previous embodiment, the oscillator 35 is connected to the rails 11 and 13 at the points 27 and 29 and at the spaced points 31 and 33, respectively. Shortcircuiting rods 95 and 97 are installed at opposite ends, respectively, of the zone of the track circuit 25, across the rails 11 and 13 and between the nearest metallic tie 91 and the adjacent wooden tie 93.

The track circuit is similar to that shown in Figs. 1 and 2,; but desirably with the addition of a condenser or capacitor 99 connected across the points 31 and 33. The circuit comprising the capacitor 71 and the rail inductances 39 and 49 ofthe track between the coupling transformers59-and 61 is adjusted so as to obtain a maximum voltage across the points 31 and 33. In order to achieve a maximum voltage across the points 31 and 33, it is necessary that the filter circuit formed from point 31, the inductance 45, the shortcircuiting bar 97, the inductance 55, to point 33, the capacitor 99, and back to point 31 be adjusted to resonance. In this manner the power furnished by the transformer 59 is utilized to the maximum for the feeding of the transformer 61 assuring that the oscillator 35 is maintained in oscillation to energize the relay 37.

A short circuit formed by the shunting action of the wheel and axle unit 23 on the inductances 43 and 53 starting from the short-circuiting bar 95 and moving towards the points 27 and 29, or on the inductances 45 and 55 starting from the short-circuiting bar 97 and moving towards the points 31 and 33 will disrupt the adjustment of the circuit and will absorb such power that the feedback energy to the oscillator 35 will be interrupted and the oscillations will cease. The relay 37 will be actuated such to control the signaling apparatus to indicate the track section is occupied. The effect will be the same for any short circuit on the inductances 39 and 49 between the points 27 and 29, and 31 and 33.

The invention is particularly applicable for use in railroad signaling systems used in conjunction with track rails Without insulating joints. The track circuit of the invention may be superimposed on another signaling system to assure supplementary functions without disturbing the circuits on which it is super-imposed and without being disturbed by them. It is also apparent that the track circuit according to my invention permits the installation of signaling apparatus of the automatic blocktype on railroad tracks having metallicor other ties.

While my invention has been described with reference to particular embodiments thereof, it will be understood that various modifications may be made by those skilled in the art without departing from the invention. The appended claims are therefore intended to cover all such modifications within the true spirit and scope of the invention.

Having thus described my invention, what I claim is:

1. A track circuit for an electrically continuous section of track rails, comprising in combination an oscillator including input and output portions, said oscillator normally being energized to oscillation, first means connecting said outputportion to said rails for coupling electrical energy thereto, and second means connecting said rails to said input portion for coupling electrical energy from said rails to said input portion, said second means connecting to said rails in spaced relation to the connections of said first means to said rails, said track circuit being shunted by railroad cars on said section of track rails to interrupt the signal energy coupled from said output portion to said input portion to cause said oscillator to cease oscillating.

2. A track circuit for a section of railroad track rails comprising in combination, an oscillator having input and output portions, a feedback path for said oscillator for connecting said output portion to said input portion, said track rails forming part of said feedback path, and the oscillation of said oscillator being interrupted by railroad cars shunting said track rails.

3. A track circuit for an electrically continuous section of track rails comprising in combination, an oscillator havin input and output portions, :1 feedback path for said oscillator for connecting said output portion to said input portion, and at least one series resonant circuit tuned to the operating frequency of said track circuit in said feedback path, said track rails forming a part of the inductances of each of the resonant circuits, the oscillation of said oscillator being interrupted by railroad cars shunting said track rails.

4. A track circuit for an electrically continuous section of track rails, said track circuit adapted for detecting the presence of railroad cars on said section of track rails, comprising in combination an oscillator having input and output portions, a feedback path for said oscillator for connecting said output portionv to said input portion, first and second resonant circuits in said feedback path, said track rails forming a part of the inductances of said resonant circuits, said oscillator being in oscillation when said track rails are unoccupied and being outof oscillation when said track rails are occupied, and relay means arranged to be controlled by said oscillator.

5. A track circuit for an electrically continuous section of track rails, said track circuit adapted for detecting the presence of railroad cars on said section, of track rails, comprising in combination an oscillator normally energized to oscillation, a first transformer having first and second windings, said second winding of said first transformer connected to said irailsfor coupling electrical energy from said oscillator to said rails, a second transformer having first and second windings, said first Winding of said second transformer connected to said rails at spaced points from the connections ofsaid second winding of said first transformer to said rails for coupling electrical energy from said rails-to'said oscillator, a first capacitor connected to said second-winding of saidfirst transformer, a second capacitor connected to said first winding of said second transformer, a first resonant circuit formed by said first capacitor, ysaidsecond winding of saidfirst transformer and the inductance of said section of track rails, and a second resonant circuit formed by said second capacitor, said first winding of said second transformer and the inductance of said section of track rails, said circuits being so proportioned such'that the presence of railroad'cars on said section of track rails affect the inductance of said resonant circuits-whereby comprising in combination, an oscillator having input and output portions, said oscillator normally energized to oscillation, afirs-t transformer having first and second windings, said second windingof said first transformer being connected to said rails for coupling electrical energy from saidoutput portion of said oscillator to said rails, a second transformerhaving first and second windings, said first winding of said second transformer being, connected to said rails at spaced points from said first transformer connections for couplingelectrical energyfrom said rails to the input-portion of said oscillator, a first capacitor connected to said second winding of said first transformer, a second capacitor connected to said first winding of said second transformer, a first resonant circuit formed by said first capacitor, said second winding of said first transformer and said section of rails, and a second resonant circuit formed by said second capacitor, said first winding of said second transformer and said section of rails,- said oscillator being in oscillation when said track rails are unoccupied, said resonant'circuits arranged to be affected by the shunting action of railroad car wheels within a predetermined zone adjacent the connections of said transformer windings to' said rails,

causing the electrical energy coupled to the input portron of said oscillator by said second transformer to be diminished and oscillation of said oscillator to cease, and relay means connected to said oscillator and arranged to be controlled thereby. r r j 1 b 7. A track circuit for an electrically continuous section of track rails, said track circuit adapted for detecting the presence of railroad cars on said section of track rails, comprising in combination an oscillator normally energized to oscillation, a first transformer having first 'and second windings, said second winding of saidfirst transformer connected to said rails for coupling electrical energy from said oscillator to sai'd rails, a second transtransformer, asecondcapacitor connected to saidgfirstformer having first and second-windings, said first wind ing of said second transformer connected to saidrails at spaced points from'the'connections of saidlsecond winding of said first transformer to said rails for coupling electrical energy from said rails to said oscillator, a first capacitor connected to said second winding of said first transformer, a second capacitor connected to said first winding of said second transformer, a first resonant circuit formed by said first capacitor, said second winding of said first transformer and the inductance of said section of track rails, and a second resonant circuit formed by said second capacitor, said first winding of said second transformer and. said section of rails, the presence of railroad car wheels within a predetermined distance of said transformer. connections to saidrailsaffecting a shunt across said rails which affects the inductive compoformer having first and second windings, said first winding of said second transformer connected to said rails at spaced points from-the connections of said second winding of said first transformer to said rails for coupling electrical energy from said rails to said'oscillator, a first capacitor connected to said second winding ofsaid first winding of said secondtransformer, a first. resonant fcircuit formed by said first capacitor, said second winding of said first transformerand the inductance of said sec-' tion of track rails, and a secondresonant circuit formed by said second capacitor, .said first'windingof said; second transformer and said section of rails, the presence of railroad car wheels within a predetermined distance of said transformer connectionsto said rails affecting a shunt across said rails which affects the inductive component of said resonant circuits whereby less energy is coupled to the input portion of said oscillator causing said OSCI]: lator to cease oscillating, relay means arrangedto be energized by said oscillator, and signaling means arranged to be actuated by said relay means. 7

9. In a track circuit for track rails of the type laid on metallic ties and in whichfwoodcn ties replace said metallic ties on a section of track rails,,a shorting bar affixed across said rails at each end of said section of rails, an oscillator'having input and output portions; first means coupling said output portion of said oscillator to said section of rails near one end thereof, second means coupling said inputportion of said oscillator to said section of rails near the opposite end thereof, and an electrical energy feedback path for said oscillator fo'rmed by said first coupling means,,said rails, and said second coupling means. l 1 V 10. In a track circuit for track rails of the type laid on metallic tics and in which wooden ties replacesaid metallic ties on a section of said track rails, a shorting bar afiixed across said rails at each end of said section of rails, an oscillator having input and outputportions, said oscillator normally being energized to oscillate a first transformer means having a first and second winding coupling said output portion of said oscillator to: said section of railsnear one end thereof, a first capacitor having one terminal connected toa first terminal of said second winding of said first transformer and having the second terminalvthereof connected to one of the'railjs, the second terminal of said secondwinding of's'aid first transformer connected to the other of said rails, aI-first e onant Circuit formed by said first capacitor said secnd winding of said first transformer, and the inductance of said rails between said shorting bars, a second transformer means having a first and second winding coupling the input portion of said oscillator to said section of rails near the opposite end thereof, a second capacitor having one terminal thereof connected to a first terminal of said first winding of said second transformer and having the second terminal thereof connected to one of the rails, the second terminal of said first winding of said second transformer connected to the other of said rails, a second resonant circuit formed by said second capacitor, said first winding of said second transformer and the inductance of said section of rails between said shorting bars,

said resonant circuits being responsive to the shunting action of railroad car wheels present on said track rails between said shorting bars to cause said oscillator to cease oscillating, and relay means connected to said oscillator and arranged to be controlled thereby.

11. In a track circuit for track rails of the type laid on metallic ties and in which wooden ties replace said metallic ties on a section of said track rails, a shorting bar afiixed across said rails at each end of said section of rails, an oscillator having input and output portions, said oscillator normally being energized to oscillate a first transformer means having a first and second winding coupling said output portion of said oscillator to said section of rails near one end thereof, a first capacitor having one terminal connected to a first terminal of said second winding of said first transformer and having the second terminal thereof connected to one of the rails, the second terminal of said second winding of said first transformer connected to the other of said rails, a first resonant circuit formed by said first capacitor, said second winding of said first transformer, and the inductance of said rails between said shorting bars, a second transformer means having a first and second winding coupling the input portion of said oscillator to said section of rails near the opposite end thereof, a second capacitor having one terminal thereof connected to a first terminal of said first winding of said second transformer and having the second terminal thereof connected to one of the rails, the second terminal of said first winding of said second transformer connected to the other of said rails, a third capacitor connected across said rails, a second resonant circuit formed by said second and third capacitors, said first winding of said second transformer and the inductance of said section of rails between said shorting bars, said resonant circuits being responsive to the shunting action of railroad car wheels present on said track rails between said shorting bars to cause said oscillator to cease oscillating, and relay means connected to said oscillator and arranged to be controlled thereby.

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